Actuator sensor never has positive pulse
There are no positive pulses on sensors. This term is a leftover from an incorrect documentation. 

A sensor has two outputs:


an evaluation result (sensor.positive) witch is either positive or not positive and gets calculated once at each single frame 
a trigger which marks all connected controllers to be executed on sensor execution (which happens after sensor evaluation)


The actuator sensor senses a specific actuator of the same object. It evaluates positive when the actuator is active and it evaluates not positive when the actuator is not active.

Be aware there are sensors that deactivate themselves within the same frame they got activated (such as property actuator, action actuator in property mode, motion actuator and state actuator).

Processing

t

The sensor detects the actuator is not active. As it was not active before it will evaluate not positive.

The actuator gets activated by a controller

The actuator runs and deactivates itself

t+1

The sensor detects the actuator is not active. As it was not active before (see t) it will evaluate not positive.

...

Conclusion

You can't measure that an actuator that immediately deactivates was running. You need other ways to detect this situation (e.g. by activating a property sensor that actually changes a property).